B
Environmental Distribution and Exposure
B.1
Equilibrium Distribution of Substances in the
Environment
As introduced in Chap. 6, substances released into the environment will be distributed and transformed through natural processes. The equilibrium distribution
of substances between environmental compartments and biota can be described
through a set of ratios described in this section. Equations for defining some of
the key rate constants that describe the speed of chemical transformation through
natural processes are also presented.
B.1.1 Air-Water
K H =
P air
c water
= R × T ×
c air
c water
(B.1)
• K H : Henry coefficient or Henry’s law constant, describes equilibrium partitioning between air and water [Pa m 3 mol −1 ]
• c water : concentration of substance in water [mol/m 3 water]
• c air : chemical concentration in the air [mol/m 3 air]
• P air : partial pressure of substance in air [Pa]
• R: universal gas constant [J mol −1 K −1 ]
• T : temperature [K]
Note: Ionic substances are so strongly hydrophilic that their concentration in the gas
phase is negligible.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
K. Hungerbühler et al., Chemical Products and Processes,
https://doi.org/10.1007/978-3-030-62422-4
265
Environmental Distribution and Exposure
B.1
Equilibrium Distribution of Substances in the
Environment
As introduced in Chap. 6, substances released into the environment will be distributed and transformed through natural processes. The equilibrium distribution
of substances between environmental compartments and biota can be described
through a set of ratios described in this section. Equations for defining some of
the key rate constants that describe the speed of chemical transformation through
natural processes are also presented.
B.1.1 Air-Water
K H =
P air
c water
= R × T ×
c air
c water
(B.1)
• K H : Henry coefficient or Henry’s law constant, describes equilibrium partitioning between air and water [Pa m 3 mol −1 ]
• c water : concentration of substance in water [mol/m 3 water]
• c air : chemical concentration in the air [mol/m 3 air]
• P air : partial pressure of substance in air [Pa]
• R: universal gas constant [J mol −1 K −1 ]
• T : temperature [K]
Note: Ionic substances are so strongly hydrophilic that their concentration in the gas
phase is negligible.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
K. Hungerbühler et al., Chemical Products and Processes,
https://doi.org/10.1007/978-3-030-62422-4
265